Django 信号 m2m_changed 未触发

在Django开发中，信号（Signal）是一种非常有用的工具，它可以在特定事件发生时发送信号，以便其他部分可以对这些事件进行响应。其中，m2m_changed信号用于在多对多关系（Many-to-Many）的关联关系发生变化时触发，即当一个模型的多对多字段的关联关系被添加、删除或清空时，m2m_changed信号将被触发。然而，有时我们可能会遇到m2m_changed信号未被触发的情况，本文将介绍可能导致该问题的原因，并提供解决方案。

python
from django.db import models
from django.db.models.signals import m2m_changed
from django.dispatch import receiver
class Blog(models.Model):
    title = models.CharField(max_length=100)
    tags = models.ManyToManyField('Tag')
class Tag(models.Model):
    name = models.CharField(max_length=50)
@receiver(m2m_changed, sender=Blog.tags.through)
def handle_blog_tags_change(sender, instance, action, **kwargs):
    if action in ['post_add', 'post_remove', 'post_clear']:
        print(f"Blog '{instance.title}' tags have been changed!")

python
from django.db import models
from django.db.models.signals import m2m_changed
from django.dispatch import receiver
class Blog(models.Model):
    title = models.CharField(max_length=100)
    tags = models.ManyToManyField('Tag', through='BlogTag')
class Tag(models.Model):
    name = models.CharField(max_length=50)
class BlogTag(models.Model):
    blog = models.ForeignKey(Blog, on_delete=models.CASCADE)
    tag = models.ForeignKey(Tag, on_delete=models.CASCADE)
@receiver(m2m_changed, sender=Blog.tags.through)
def handle_blog_tags_change(sender, instance, action, **kwargs):
    if action in ['post_add', 'post_remove', 'post_clear']:
        print(f"Blog '{instance.title}' tags have been changed!")